Abstract: Aims As a crucial coupling agent linking plant roots, soil, and microorganisms, root exudates serve not only as an important vector for information transformation, but also as the core carrier for energy input, playing a significant role in shaping responses of plants to environmental changes. However, the effects of mixed-species on the metabolite compositions of root exudates remain unclear. Our objective is to explore the differences in metabolite compositions of root exudates between mixed-species stands and corresponding pure stands, and the implications on sustainable management of subtropical plantations. Methods In this study, we used in-situ collection devices to sample root exudates of Pinus massoniana and Erythrophleum fordii in their pure and mixed (P. massoniana×E. fordii) stands in southern subtropial China. The metabolite compositions of root exudates of each species were analyzed using LC-MS/MS. Important findings (1) The relative quantitative values of lipids, organicheterocyclic, organic acid and organic oxygen compounds in root exudates of Pinus massoniana and Erythrophleum fordii were significantly higher in pure stands than in mixed stands. (2) Comparative analysis of differential metabolites between pure and mixed stands revealed that P. massoniana had 208 differential metabolites, with glycerophospholipids exhibiting significant up-regulation in the P. massoniana pure stand. E. fordii had 106 differential metabolites, with p-Mentha-1,8-dien-7-ol, chavicol, isobutyric acid and diplodiatoxin exhibiting significant up-regulation in the E. fordii pure stand. (3) KEGG annotation and enrichment analysis showed that lipid metabolism pathways were significantly up-regulated in both P. massoniana and E. fordii pure stands compared to the mixed stand. Lipid metabolism was correlated with plant defense strategies.

Key words: Root exudate, Metabolite composition, Pure plantation, Mixed plantation, Southern subtropical China